The invention herein is concerned generally with sealing nuts and more particularly with a sealing nut having the ability to withstand extremely high pressures.
The particular environment in which the nut of the invention is intended for use is one which poses stringent requirements. The environment comprises a hydraulic chamber which is subject to internal pressures above 20,000 p.s.i. having a threaded stud or other threaded member extending through a threaded passageway in the wall of the chamber, it being desired from time to time to rotate the threaded stud for reasons which are of no concern to this invention. Hydraulic fluid deteriorates many substances; the environment may be subject to heat which may reach over 90.degree. C.; the nut may have to be loosened and tightened often; the pressure may have to be contained over a considerable length of time. There are other considerations related to the general need for a locking and sealing nut of this kind.
The sealing nut of the invention has a wide range of utility in other environments as well as the particular one which is mentioned above, this being in connection with hydraulic brake systems for highway vehicles.
Prior sealing arrangements have included many different types of structures which had various disadvantages. These need not be exhaustively discussed, but a brief mention of some will emphasize the advantages of this invention.
The so-called elastic stop nut structure which is generally represented by the embodiment described in U.S. Pat. No. 2,450,694 was primarily intended as a locking device. Its nylon insert was unthreaded so that when first used the thread was formed by the act of screwing the nut home. This gave a small degree of sealing, but only between the male threaded member and the nut. This type of nut is not readily "spun" either in installing or removing the same since the thread-to-thread clearance at the insert is practically nothing. These nuts are not as effective, if at all, in re-use as they are for their initial use. Threading the nylon insert during manufacture substantially eliminates their locking and sealing abilities.
The use of a non-threaded insert in large nuts makes these nuts difficult to install and remove.
It is clear that there is no sealing ability for the elastic stop nut in any assembly of the type which has been referred to at the outset of this discussion, that is, at the axial end when the nut is brought into engagement with a bearing surface through which the threaded male member protrudes. Washers or other means are required to effect such sealing. Besides the inconvenience of handling, such means may be destroyed or rendered non-reusable when the amount of torque applied is high as in the case of vary high pressure installations. For example, a 5/8 inch nut of the invention is installed initially with a torque of between 50 and 70 foot-pounds. This will extrude many types of compounds which would be used as washers.
The art has gone to the confining of the sealing member, this being disclosed in U.S. Pat. Nos. 3,265,107, 3,572,414 and 3,635,272. These structures utilize inserts of a material which is generally extrudable in order to press portions of the insert into engagement with the various parts of the assembly.
In U.S. Pat. No. 3,265,107 the sealing to be effected is in the opening of a sheet metal member and the insert is resilient, being of silicone rubber or the like. It is hence readily distortable and capable of being configured to radically different shapes compared with its original one. For high pressures and an insert made of stiff nylon, even though the material permits a degree of cold flow, this structure would not be practical. The type of nylon required for high pressure arrangements is not readily compressible, if at all, and it is likely to shear before the metal-to-metal contact is achieved if a structure like that of this patent were attempted. Compressing the nylon would take enormous torque.
In U.S. Pat. No. 3,572,414 the insert is made of a low durometer urethane rubber and the need for preventing almost liquid flow of this material from its confining recess dictates a structure that leaves little of the material for sealing purposes. The use of such material and the structure disclosed in high pressure installations would be ineffectual.
In U.S. Pat. No. 3,635,272 the insert is bonded into its recess by pre-molding and then heating the nut. This is an expensive process and could well change the physical characteristics of the nut - especially if the temperature must be elevated enough to seal an insert of small size in a large nut. In addition to that disadvantage, the material used is said to be nylon or other polyamide resin capable of flowing under pressure into six recesses circumferentially arranged around the nut. A stiff material such as needed in high pressure installations would not flow as readily. In an installation such as intended by this patent, where the bolt shank enters a drilled passageway and not into a threaded passageway, if the insert were of the stiff type needed for high pressure, the corner of the passageway, although chamfered, would be likely to punch a ring out of the insert before it permits it to flow as described.
The inserts of two of the above mentioned prior art patents cannot be threaded internally unless they are bonded in place, because otherwise they will rotate if attempt is made to tap them when the nut is tapped. Threading them apart from the nut is impractical because the threads would not match those of the nut when assembled. Only U.S. Pat. No. 3,572,414 shows the insert locked in place, and it is not internally threaded.
As will be explained, the insert of the nut of the invention is formed independently of the nut body and before the nut body is tapped. It is formed of a type of nylon which has a lubricant that is compounded in it primarily for the purpose of enabling it to release readily from molds. Coincidentally, the lubricating qualities assist in the taking up of the nut during its last stages of installation. Such a material cannot be molded and bonded into a recess as proposed by the prior art because it will fall out. Certainly if attempted to be secured by some expensive means such as adhesive it cannot help but be displaced during the tapping process.
To have a substantial protruding part and still secure the insert mechanically into the nut body while at the same time providing a space for the displacement of the protruding part during installation is not taught by the prior art so far as known. The displacement is a substantial one in order to effect the seal and lock and the way of doing this with a stiff insert material and without raising other problems is also not taught in said prior art.
The structures of the prior art which involve the use of confined inserts have not displaced one of the principal methods of assuring a seal in the high pressure hydraulic field. The method in common use at this time involves forming a recessed seat in the surface of the body through which the male threaded member is to be screwed, surrounding and coaxially with the threaded member. An 0-ring or other sealing member to be confined is installed in the recess and adapted to be compressed by the nut, either with or without a washer. Several such 0-rings may be used. This type of structure is expensive and the 0-rings must be replaced frequently.
The invention herein is ideally suited for use in the high pressure hydraulic field, but its principles are applicable in other fields where the requirements to achieve sealing are not as great. This is because of the great economy and effectiveness. This is true aside from the fact that it eliminates the need for surface recesses, washers and 0-rings.
The most important difference between the sealing nut of the invention and the prior structures is that the substantial protrusion of the insert (called a "crown") herein is not intended to be only extruded and/or compressed during the take-up action of the nut, as in the prior art, but instead is folded outwardly upon itself initially. Thus, a substantial displacement is achieved without the need for expenditure of large amounts of energy, meaning that great torques need not be applied in the early stages of assembly. The crown is made relatively narrow, i.e., measured radially, so that there is enough space to enable the formation of a shoulder to provide for securement of the insert into a socket by coining a lip onto the shoulder while still leaving space (called a "gallery") for the folded end of the crown to seat. After this has occurred and the axial end of the lip approaches the metal-to-metal contact desired, the body of the insert is compact ready to receive the pressure for causing the necessary cold flow to effect sealing. At this time, the maximum of torque is applied.
The manufacture of the nut is highly economical since the inserts are molded independently in production, the nut bodies formed in a manner not differing substantially from that used to make the bodies of elastic stop nuts, the inserts installed in the sockets, the lips coined and the nuts tapped. The folded crown may be preformed prior to the nut being tapped by deflecting the crown outwardly.
As stated above, the nut of the invention is especially intended for use in the high pressure hydraulic field but its principles are also applicable in circumstances where the requirements are less stringent. This should not be considered to detract from the many features and advantages which are achieved specifically in the high pressure hydraulic field.
In order to indicate the benefits and advantages of the nut of the invention when used in the high pressure hydraulic field there follows a list of the features achieved through the practice of the invention in that field. In considering this list, it will be apparent that the nut of the invention is also applicable where instead of a so-called "wet" environment existing on the interior of a chamber through the wall of which a threaded male member is adapted to be screwed, the environment may be "dry" but under gaseous pressure. Unless the gas is corrosive, the problem of the deterioration of the insert caused by hydraulic fluids and the like is eliminated.
The features which are set forth are the principal ones, there being many others of a minor and indirect nature (not necessarily in the order of importance):
(1) The sealing material is rugged, stiff, durable and yet has a sufficient degree of flow to achieve the necessary sealing and locking.
(2) There is a substantial displacement of the crown of the insert without requiring undue torque and without damaging the insert during such displacement.
(3) The insert is permanently locked into the body of the nut, this being accomplished by machinery and methods used to form elastic stop nuts of conventional construction.
(4) There is a space (gallery) into which the displaced portion of the crown enters towards the end of the take-up action.
(5) There is a metal-to-metal contact of the nut body against the bearing surface after the nut has been fully taken up at which time the insert material is fully confined and has been forced to flow into the areas where the sealing must be effected.
(6) The nut and its insert are tapped with a continuous thread during manufacture so that the nut can be spun on the male threaded member to the point where the actual taking up can be commenced.
(7) The nut is reusable in that notwithstanding it has been torqued home and has effected a seal and a locking, it can be unscrewed readily, is readily backed off without the need for application of any substantial torque and can thereafter be reinstalled with as much sealing and locking efficiency as before.
(8) The seal is such as to withstand extremely high pressures without leakage.
(9) The nut has an indefinite shelf life since the insert material does not deteriorate. This also means that when installed and maintained under pressure for a long period of time there is no relaxation which could give rise to leakage because, in addition to the nature of the material of the insert, it is confined and not readily capable of cold flowing past the limits established by the act of compression in achieving the metal-to-metal contact.
It should again be emphasized that the economy with which the nut of the invention can be made and its effectiveness make it well suited to form other applications in addition to sealing in the high pressure hydraulic field.